It's a pan that fits into another pan to keep the direct heat off what you're cooking.

If you don't have one, use a pan half full with boiling water and a metal bowl on top of it.

Combine sugar, flour and salt in top of double boiler. Add milk slowly, mixing thoroughly. Cook over rapidly boiling water until well thickened, stirring constantly.

Cook 10 minutes longer, stirring occasionally.

Stir a small amount of the hot mixture into egg yolks, then pour back into remaining hot mixture while beating vigorously. Cook 1 minute longer.

Remove from heat and add butter and vanilla. Cool.

You can use a pie shell or crush it for a bottom crust. You can also use crushed graham crackers or vanilla wafers as a bottom crust as well. If you use the bottom crust, make sure to spray the side of the pie pan with non-stick spray.